The present invention relates to an improved catalytic hydrocarbon oxidation process to obtain maleic anhydride from butane.
Catalysts for use in oxidation of hydrocarbons are well known and the production of dicarboxylic acid anhydrides by vapor-phase catalytic oxidation is well known. Suitable processing conditions for the use of these catalysts in oxidation processes such as partial oxidation processes to convert benzene, butene, butane, and other hydrocarbons to maleic anhydride are also well known.
A series of patents to Kerr, including U.S. Patents 3,156,705; 3,156,706; 3,156,707; 3,238,254; 3,255,211; 3,255,212; 3,255,213; 3,288,721; 3,351,565; and 3,385,796 disclose phosphorus-vanadium oxide catalysts for vapor-phase oxidation of butene to maleic anhydride. For example, Kerr U.S. Pat. No. 3,156,705 discloses a catalyst comprising phosphorus and vanadium oxides wherein an additional component is included in the catalyst as a phosphorus stabilizer, which stabilizer is said to improve the life of the catalyst.
The Kerr references suggest the use of catalysts with a surface area below 5 m.sup.2 /g. Thus Kerr U.S. Pat. No. 3,288,721 states at columm 5, lines 12-16:
"The catalyst support, if used, provides not only the required surface for the catalyst, but gives physical strength and stability to the catalyst material. The carrier or support normally has a low surface area, as usually measured from about 0.001 to about 5 square meters per gram."
The suggestion of low surface area for the hydrocarbon oxidation catalyst is consistent with other prior art, which suggests the use of low surface area catalyst for hydrocarbon oxidation catalysts. Thus, in an article by C. F. Cullis, entitled "Heterogenous Catalytic Oxidation of Hydrocarbons" (Ind. & Eng. Chem. 59 [12] 18 (1967)), on page 21 it is stated: "...the best oxidation catalysts have large diameter pores and are generally of fairly low surface area." By "hydrocarbon oxidation catalysts" it should be understood that reference is to catalysts for the partial rather than complete oxidation of hydrocarbons all the way to carbon oxides.
Bergman U.S. Pat. No. 3,293,268 discloses a vanadium-phosphorus oxide catalyst for butane oxidation to maleic anhydride.
U.S. Pat. No. 3,846,280 to Schneider discloses a catalyst comprising vanadium-phosphorus oxides for use in catalytic oxidation of hydrocarbons, such as butane, to maleic anhydride. The catalysts used in the Schneider process have a relatively high surface area, preferably above 7 square meters per gram.
Defensive Publication No. 784,946 describes reactivation of oxidation catalysts which have been exposed to excessive heat. The catalysts--for example, ammoxidation catalysts--are reactivated using a reducing gas such as propylene.
U.S. Pat. No. 1,896,031 discloses reactivation of an oxidation catalyst using a reducing gas; the reducing gas of Example 1 being 3% toluene, 15% air, 2% ammonia and 80% coal gas.
U.S. Pat. No. 2,500,776 discloses reactivation of an ammoxidation catalyst using high-temperature hydrogen.
Netherlands Patent Application No. 73/14746 is directed to an improvement in a process for the preparation of maleic anhydride wherein n-butane is oxidized with a gas containing molecular oxygen in the presence of a phosphorus-vanadium-oxygen complex catalyst and wherein the catalyst deactivates under conditions of high temperature. According to Netherlands 73/14746 the activity of the deactivated catalyst is restored by periodically contacting the catalyst with a reducing agent. Reducing agents disclosed are hydrogen, methane, carbon monoxide and hydrogen sulfide gases.